Packing source data packets into transporting packets with fragmentation

ABSTRACT

A communication system and method are disclosed for transmitting packets of information in at least one first format over a communications link that utilizes packets of information in a second format. In certain embodiments, the packets of information in a first format are converted to packets of information in the second format prior to transmission via the communications link by packing and fragmenting the information in the first format in a coordinated manner. Embodiments may also utilize packing subheaders and fragmentation control bits in the packing and fragmentation processes.

RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 14/831,387 filed Aug. 20, 2015; which is a continuation of U.S.application Ser. No. 12/886,323 filed Sep. 20, 2010, issued as U.S. Pat.No. 9,119,095, issued Aug. 25, 2015; which is a continuation of U.S.application Ser. No. 10/053,179 filed Jan. 15, 2002, issued as U.S. Pat.No. 8,009,667, issued Aug. 30, 2011; which claims priority to U.S.Provisional Application No. 60/262,005, filed on Jan. 16, 2001, all ofwhich are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to packet data communications systems, andreformatting data in such systems before transmitting the data through alink.

2. Description of the Related Art

Data communications systems typically transfer data from a source to anend user by routing the data in packets through communications links.All links have physical limits on their data-carrying capacity, orbandwidth. It is a constant pursuit to most efficiently utilize thefinite capacity of any communications link in an effort to increase datathroughput.

Many varieties of communications systems exist with a variety ofdifferent protocols governing their transmission of data. Theinformation transmitted in many of these systems is transmitted indiscrete packets of data. For each system these packets may be of astandard length or may vary in length as the needs of the users dictate,but the format of the packets are generally unique to the protocolutilized. Data packets utilizing a particular protocol and format may bereferred to as service data units, or SDUs. An exemplary format,Internet Protocol or EP format, permits flexibility in the routing ofdata between a source and a destination, while other formats may conveyvoice data with limits on time delays, so as to ensure that the voicedata can be reconstructed with adequate fidelity at the receiving end.It is often desirable for data in various formats to utilize the samedata links as part of their transmission paths. This is particularlytrue for links directed to solving the problem of connecting end usersto the various communications networks that are the source of datasought by those users, known as the “last mile” problem. Solutions forthe “last mile” problem tend to attempt to satisfy, to the greatestextent possible, the needs of the users, while supporting the variousprotocols and packet formats that the data may utilize. While thesesolutions often involve various processes, it is often true that mostcommunications links utilize a specific data packet format and protocolof their own to most efficiently utilize those links; the protocol datapackets utilized by these links may be referred to as Protocol DataUnits or PDUs. It is an ongoing effort in the data communicationsindustry to maximize the efficiency of communications links having afinite bandwidth while maintaining the integrity of the protocol andformat of the SDUs being transported by those links.

SUMMARY OF THE INVENTION

The systems and methods have several features, no single one of which issolely responsible for its desirable attributes. Without limiting thescope as expressed by the claims which follow, its more prominentfeatures is now discussed briefly. After considering this discussion,and particularly after reading the section entitled “DetailedDescription of the Preferred Embodiments” one will understand how thefeatures of the system and methods provide several advantages overtraditional communications systems.

In one aspect, the invention relates to a system and method offormatting data arriving in SDUs of various formats into differentpackets, having a PDU packet format, for transport across acommunications link, comprising packing one or a plurality of fragmentsof arriving SDUs or whole SDUs into single PDU packets.

Within the above aspects, the plurality of SDUs may have differentlengths, with a length of at least some of the SDUs reflected inrespective packing subheaders. The packing subheaders may be madecontiguous with the SDUs whose length within the PDU they reflect, or inanother aspect may be separated from the SDUs. Other aspects include theforegoing systems or methods, further providing at least twofragmentation control bits in a header of the PDU. The fragmentationcontrol bits may indicate absence or the presence and orientation of anyfragments in the PDU.

Another aspect can be embodied in any packeted data communicationsnetwork. For example, the aspect may be embodied in a broadband wirelesslink that connects a plurality of end users to various networks.

In another aspect, a millimeter wavelength wireless RF channelcommunications system connecting single base stations to a plurality ofrelatively proximate nodes can be utilized. A network of such basestations with their surrounding nodes can provide communicationsservices over a large area, such as a city. Such a system isrepresentative of a variety of communications links having a limitedcommunications media which must be shared by a plurality of differententities. Such systems may include wire connected informationdistribution systems such as, for example, Dial-up or DSL systems,visible light spectrum data transmission systems, and microwave datatransmission systems among others.

In yet another aspect, a method is disclosed of packing data prior totransferring it through a communications link while utilizing theadvantages of fragmentation of SDU packets, and coordinating the twomethods to optimize the advantages of each. Incoming SDU data packetsthat have been formatted according to a first, second or other protocol,such as ATM standard format or Internet Protocol (IP) or any otherprotocol, are compressed and reformatted and then conveyed over one ormore links in accordance with a second PDU protocol, such as, forexample, variable length packet MAC protocol. After it has traversed thelink, the data may be reconstructed back into the first protocol formatso that the data modifications performed by the link will be transparentto the receiving node or user.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a high level illustration representing an overallcommunications network and system.

FIG. 2 is a high level functional block diagram of an exemplary basestation. FIG. 3 is a high level functional block diagram of an exemplarynode.

FIG. 3 is a high-level block diagram of the functional modules of anexemplary node.

FIG. 4 is an illustration of the breakdown of a frame in communicationssystems utilizing frames.

FIG. 5 is an illustration of the Downlink mapping of messages from PHYelements to PDUs in one embodiment.

FIG. 6 is an illustration of the Uplink mapping of messages from PDUs toPHY elements in one embodiment.

FIG. 7 is an illustration of an information hierarchy from sectortransmission to modulation group information to connection breakdown inan exemplary transmission link frame.

FIG. 8 is an illustration representing a sample PDU header andillustrating the various fields the PDU header might have.

FIG. 9 is a functional block diagram of components that process andtransfer data in an exemplary base station communications processor.

FIG. 10 is functional block diagram of components that handle controlfunctions in an exemplary base station communications processor.

FIG. 11 is a functional block diagram of components that process andtransfer data in an exemplary node communications processor.

FIG. 12 is functional block diagram of components that handle controlfunctions in an exemplary node communications processor.

FIG. 13 is a flow chart illustrating the steps of an exemplary processfor forming PDUs from incoming SDUs.

FIG. 14 is an illustration demonstrating the relationship between thePDU header, the payload and the PDU subheader.

DETAILED DESCRIPTION

Embodiments of the invention are now described with reference to theaccompanying figures, wherein like numerals refer to like elementsthroughout. The terminology used in the description presented herein isnot intended to be interpreted in any limited or restrictive mannersimply because it is being utilized in conjunction with a detaileddescription of certain specific embodiments of the invention.Furthermore, embodiments of the invention may include several novelfeatures, no single one of which is solely responsible for its desirableattributes or which is essential to practicing the inventions hereindescribed.

Communications networks often need to transport data in a variety ofdifferent formats. It is therefore useful if communications systems thatprovide links within an overall communications network are able toaccept data in a first or second format such as ATM or IP, or many otherformats such as voice communications, Ti, El, or any other format commonin the art. However, it is also useful for many communications systemlinks to have a particular preferred format for all transported data inorder to most efficiently utilize the link capabilities. To harmonizethese two advantages, it is often desirable that a linking ortransporting communications system accepts data in many formats andconverts the data into a transporting format for transport across thelink. At the far end of the link, the reformatted data may be returnedto its original format. In this process of reformatting, incoming dataarrives as SDUs (Service Data Units), which may be in any of the abovementioned formats, and will be converted to PDUs (Protocol Data Units)having a format desirable for a linking communications system. It isdesirable to fit the SDUs efficiently into the PDUs to enhance the datacarrying capability of the communications system link transporting theincoming data SDUs.

An example of a communications system that provides links for use withinoverall communications networks is described in copending U.S. patentapplication Ser. No. 09/702,293, entitled “COMPRESSION OF OVERHEAD INLAYERED DATA COMMUNICATION LINKS,” filed Oct. 30, 2000 (the '293application), which is hereby incorporated by reference. The methodsdescribed herein may be employed with the system modules described inthe '293 application to form an improved system for transporting dataacross a communications link. Appropriate functional modules describedin the '293 application employing the specific methods of packingdescribed below form a system and apparatus for packing SDUs intotransport system PDUs that have the capacity to carry SDU fragments,which are portions of SDUs. Fragmenting is a method of partitioning apacket of data into two or more smaller pieces to be conveyed over acommunications link that utilizes packets; and it is accomplished whenthe packet is too large for the existing bandwidth of a current frame orcommunications cycle.

FIG. 1 is a high level illustration representing an overallcommunications network and system. FIG. 1 depicts a representativenetwork for transmitting data packets from a data source to end-usersand vice versa. While FIG. 1 depicts a system utilizing a wireless linkbetween a base station 12 and nodes 16, this is only exemplary and anytransmission link, such as electrical conductors, RF waves, microwaves,optical fiber conductors, and point to point/multipoint lighttransmission links, can be used. The communications domain of the basestation 12 in FIG. 1 is directional and is broken up into four sectors14 with each sector 14 capable of containing multiple nodes 16. Althoughthe base station of FIG. 1 provides for four sectors 14, the basestation 12 may be non-directional, having no sectors 14, or may havemore or less than four sectors 14.

Within each sector 14 or transmission area of the base station 12 theremay be any number of nodes 16. The base station 12 may utilize one ormore modulation and error correction schemes with which to transmit andreceive signals at varying degrees of reliability and bandwidth. Thewireless system 10 exemplified in FIG. 1 may utilize Time DivisionDuplexing (TDD), Frequency Division Duplexing (FDD) or any otherduplexing or multiplexing, as well as any other type of communicationslink modulation or segmenting scheme. For simplicity of explanation, aTDD system will be made reference to hereinafter. As illustrated, somenodes 16 may utilize QAM-4 while others utilize QAM-16 and QAM-64; butthe illustrated division between the nodes 16 is only exemplary and themodulation scheme utilized by any particular base station 12 may dependupon the connection establishing and monitoring routine and protocol ofthe particular system 10.

The highlighted sector 14 contains five nodes 16 with each node 16serving multiple connections for users. The users may be a servicenetwork such as a LAN, WAN, Intranet, Ring Network or other type ofnetwork; or they may be a single user such as a work station. The basestation 12 is advantageously connected to various data sources such asthe internet, other communications networks or any number of data bases,or any other data source. Information is received by the base station 12from the data source, is prepared for and transmitted across a data linkto a node 16, and is then directed to the appropriate connection fortransmission to the appropriate user.

Information is advantageously passed in the opposite direction as well,from user to data source.

Within the sectors 14, the downlink transmissions from the base station12 are typically multiplexed, and each node 16 within a particularsector 14 can receive the same transmission from the base station 12.Each node 16 may await its particular information indicated by somecontrol means and then process only the information contained therein;or alternatively each node 16 may receive all of the data within itsmodulation group and discard any data not pertinent to the users on itsconnections. Nonetheless, each node 16 has a distinct “virtual”connection, or communications link, within its sector 14. A link conveysthat part of the downlink transmissions within the sector 14 from thebase station 12 that contains data for the particular node 16, and alsoconveys uplink transmissions from the particular node 16 to the basestation 12. Nodes 16 in other sectors 14 likewise communicate to basestation 12 through links that are virtual connections within thetransmissions of their particular sector 14. The transmissions ofdifferent sectors 14 are independent of each other. “Sectorized”transmission permits spectrum reuse within a narrow area, thus providingmore bandwidth to service particular users.

FIG. 2 is a high level functional block diagram of an exemplary basestation and illustrates the functional modules that may be used. Theterm “module,” as used herein, means, but is not limited to, a softwareor hardware component, such as an FPGA or ASIC, which performs certaintasks. A module may advantageously be configured to reside on anaddressable storage medium and configured to execute on one or moreprocessors. Thus, a module may include, by way of example, components,such as software components, object-oriented software components, classcomponents and task components, processes, functions, attributes,procedures, subroutines, segments of program code, drivers, firmware,microcode, circuitry, data, databases, data structures, tables, arrays,and variables. The functionality provided for in the components andmodules may be combined into fewer components and modules or furtherseparated into additional components and modules. Additionally, thecomponents and modules may advantageously be implemented to execute onone or more computers.

A base station 12 may comprise a communications processor 20, a modem22, an antenna 24, an input/output (I/O) control 26, and an IF/RFconverter 30. These modules indicate certain functions but are notintended to indicate any particular architecture. In fact, the functionsrepresented by these modules may be combined into a single module, intomultiple modules or any combination thereof, with the illustration inFIG. 2 providing only an exemplary arrangement of one way in which tocarry out those functions.

The communications processor 20, or converter, fulfills many functionsas described below and provides most of the control functions occurringwithin the base station 12. During downlink transmissions, the datasources provide data in the form of SDUs to the base station 12 via thebackhaul interface 28, which forms the connection between the datasources and the base station 12. The I/O control 26 controls thetransfer of SDUs between the base station 12 and the data sources viathe backhaul interface 28. The I/O controller 26 transfers the SDUs fromthe backhaul interface 28 to the communications processor 20, whichamong many other things, converts them to PDUs of a protocol format thatis appropriate for the transmission link. The communications processor20 transfers the PDUs to a modem 22, which converts them to anintermediate transmission modulation or frequency for an RF link system,and passes them on to an IF-RF converter 30. The IF-RF converter 30converts intermediate frequency signals provided by the modem 22 to anappropriate frequency required for transmission before passing them tothe antenna 24. In a system that does not utilize an RF link, this stepmay not be necessary, or may take another form that is appropriate forthat medium. The antenna 24 preferably receives signals from the IF-RFconverter 30 at a radio frequency, or transmission frequency, andtransmits them. For systems that do not utilize an RF link, othersuitable transmission mechanisms are utilized. In other words, thefunction provided by the IF-RF converter 30 and antenna 24 may generallybe thought of as that of a transmitter in any system, wireless or not.

During uplink transmissions, the antenna 24 receives RF signals from oneor more nodes 16 and transfers them to the IF-RF converter 30. The IF-RFconverter 30 converts signals provided by the antenna 24 to anappropriate frequency range for the modem 22 to process. The generalfunction performed by the antenna 24 and the IF-RF converter 30 may bethought of as that of a receiver in this or other systems. For nonRFsystems, comparable modules would perform these functions to prepare thereceived signals for the modem 22. The modem 22 demodulates the signalfrom the IF-RF converter 30 and transfers a digital signal comprised ofPDUs to the communications processor 20. The communications processor 20receives the digital signal from the modem 22 and, among other things,converts the signal into the SDUs that the users had transmitted to thenode 16. The SDUs are then sent to the PO control 26 for transfer out ofthe base station 12. The I/O control 26 transmits the SDUs to theappropriate data source via the backhaul interface 28.

FIG. 3 is a high-level block diagram of the functional modules of anexemplary node. A node 16 may include a communications processor 32, amodem 40, an IF-RF converter 42, an antenna 44, and a connectioninterface 34 coupled to a plurality of user connections 36. Thesemodules indicate certain functions, but are not intended to indicate anyparticular architecture. The functions may be fulfilled by anyparticular module alone or in any combination. Alternatively, a singlemodule may accomplish all of the functions.

During downlink transmissions, the PDUs are transmitted from the basestation 12 to the node 16 and are received at the node 16 by the antenna44, for RF systems. Systems not using RF communications links would usea receiver having analogous receiving components. The antenna 44converts the RF signals received into electronic signals which are thentransferred to the IF-RF converter 42. The IF-RF converter 42 convertsthe signals from the transmission frequency to an intermediate frequencyand transfers those signals to the modem 40. The modem 40 furtherdemodulates the intermediate frequency signals into a digital signalthat includes PDUs. The digital signal including PDUs that are thentransferred to the communications processor 32, or converter, which thenconverts the PDUs back into the SDUs that were sent to the base station12 by the data source(s). The SDUs are then directed to the connectioninterface 34, which directs the SDUs to the appropriate user connection36. The SDUs can then be directed to the appropriate users via the userconnections 36.

During uplink transmissions, information packages in the form of SDUsare provided by the user connections 36 to the connection interface 34.The connection interface 34 is utilized by the communications processor32 to control the transmission of SDUs to the node 16 and transfers theSDUs to the communications processor 32. The communications processor32, among other things, converts the SDUs into the appropriate PDUformat for the transmission link. The PDUs are then transferred from thecommunications processor 32 to the modem 40, which modulates them ontoan IF carrier signal. The modem 40 transfers the IF signal to an IF-RFconverter 42, which further converts the signal to the RF range that isappropriate for the antenna 44 or other transmitting mechanism. Again,if an RF communications link is not being utilized, the IF-RF converter42 and the antenna 44 may be substituted by an appropriate transmitterfunction module. This function is that of a transmitter and any suitabletransmitter may be used. The RF signal is then transmitted via theantenna 44 across the comminations link to the base station 12 forprocessing and transference to an appropriate data source as discussedabove.

FIG. 4 is an illustration of the breakdown of a frame in communicationssystems utilizing frames. FIG. 4 shows a TDD frame and multi-framestructure 200 that may be used by the communications system 10 ofFIG. 1. As shown in FIG. 4, the TDD frame 200 is subdivided into aplurality of physical slots (PS) 204, 204′. In one embodiment, the TDDframe 200 is one millisecond in duration and includes 800 physicalslots. Alternatively, the present invention can be used with frameshaving longer or shorter duration and with more or less PSs. Some formof digital encoding, such as the well-known Reed-Solomon (RS) encoding,convolutional encoding, or turbo code encoding, may be performed on thedigital information over a pre-defined number of bit units referred toas physical layer information elements (PI). The modulation and/or theFEC type may vary within the frame and determines the number of PSs (andtherefore the amount of time) required to transmit a selected PI. In oneembodiment, data is referred to as being sent and received using threedifferent modulation types, namely, QAM-4, QAM-16, and QAM-64.

In alternative embodiments, other modulation types, FEC types, orvariation of a modulation or FEC type may be used. For example, an RSencoding system may use different variations of block sizes or codeshortening; a convolutional encoding system may vary the code rate; anda turbo code system may use any block size, code rate, or codeshortening. To aid periodic functions, multiple frames may be groupedinto multiframes 206, and multiple multiframes 206 may be grouped intohyper-frames 208. In one embodiment, an Adaptive Time Division Duplex(ATDD) system may be implemented. In ATDD mode, the percentage of theTDD frame allocated to downlink versus uplink is a system parameter thatmay change with time. In other words, an ATDD system may vary the ratioof downlink data to uplink data in sequential time frames.

FIG. 5 is an illustration of the downlink mapping of messages from PHYelements to PDUs in one embodiment. FIG. 5 shows one example of a TDDdownlink subframe 300 that can be used by the base station 12 totransmit information to the plurality of nodes 16. The downlink mappingillustrated in FIG. 5 can be performed by the communications processorin the base station, and is performed to map PDUs of varying lengths tothe PSs utilized by a wireless communications system as described abovewith reference to FIG. 4. As mentioned previously, in a TDD system, eachtime frame is divided into a downlink subframe and an uplink subframe.More specifically, during each frame (or other predetermined period),the downlink subframe is first transmitted from the base station 12 toall nodes 16 in the sector 14, after which the uplink subframe isreceived by the base station 12 from particular nodes 16. The downlinksubframe 300 may be dynamic, such that it may be different in sequentialtime frames depending on, among other things, an uplink/downlink splitdetermined by the communications processor 20. In an FDD system, thetime frame is not divided between uplink and downlink data. Instead, anFDD downlink subframe is an entire frame of downlink data on a firstchannel, and an uplink subframe is an entire frame of uplink data on asecond channel. In a typical FDD system, the downlink subframe anduplink subframe may be transmitted simultaneously during the samepredetermined period. Thus, in an FDD system both the base station 12and the nodes 16 may receive and transmit at the same time, usingdifferent channels. In another embodiment, the downlink subframe anduplink subframe may not be transmitted at the same time, but still usedifferent channels.

The downlink subframe 300 of FIG. 5 preferably comprises a frame controlheader 302 and a plurality of downlink data PSs 204. The plurality ofdata PSs may be grouped by any combination of modulation type, FEC type,node index, and connection ID and may also be separated by associatedmodulation transitions (MTs) 306. MTs separate differently modulateddata, and a transmit/receive (Tx/Rx) transition gap 308. MTs may be agap, a period of time to allow for the transition from one modulationgroup to the next. Alternatively, that transition can occur at theboundary between the last PS of one modulation group and the first PS ofthe next modulation group. In any downlink subframe, any one or more ofthe differently modulated data blocks may be absent. In one embodiment,MTs 306 are 0 (“zero”) PSs in duration. The frame control header 302 maycontain a preamble that can be used by the physical protocol layer (PHY)for synchronization and equalization purposes. The frame control header302 also includes control sections for both the PHY and the PDU protocolcontrols. An FDD downlink subframe may be substantially identical to thestructure of FIG. 5, but without a Tx/Rx transition gap 308.

The downlink data PSs 304, 304′ are advantageously used for transmittingdata and control messages to the nodes 16. This data is preferablyencoded (using a ReedSolomon encoding scheme, or other scheme forexample) and transmitted at the current operating modulation used by theselected node 16. In one embodiment, data is transmitted in apre-defined modulation sequence, such as QAM-4, followed by QAM16,followed by QAM-64. The MTs 306, if present, are used to separate themodulation schemes to synchronize the base station 12 and the nodes 16.The PHY control portion of the frame control header 302 preferablycontains a broadcast message to all of the nodes indicating the identityof the PS 304 at which the modulation scheme changes. The ordering ofmodulation groups in the transmission subframe illustrated in FIG. 5 isonly an example and any ordering of modulation groups may be used;alternatively, the order may change from frame to frame depending on theneeds of the system. Finally, as shown in FIG. 5, the Tx/Rx transitiongap 308 separates the downlink subframe from the uplink subframe. Whilethe present embodiment illustrates the use of a gap to transition fromuplink to downlink, systems may be equipped so as to identify thetransition without the use of gaps.

FIG. 5 also shows an embodiment of a three-stage mapping process from astream of variable length PDUs or user messages, to 228-bit TC DataUnits (TDUs) 500, otherwise known as a TC/PHY packets 500, to 300-bitPIs and finally to 25-symbol PSs (PIs and PSs are described above withreference to FIG. 4). The illustration and description of the processfor conversion of SDUs into PDUs is discussed in detail later.

In one embodiment, a minimum physical unit that the system allocates isthe 25-symbol PS 304, 304′. The minimum logical unit the exemplarysystem of FIG. 5 allocates may be a 208-bit (26-byte) payload of the228-bit TC Data Unit (TDU) 500. Other embodiments can be used that havedifferent minimum quantities of the physical and logical units withoutdeparting from the scope of the present invention.

Alternatively, information mapping processes may take different stepsbetween PDU formation and transmission. For instance, the last TDU (andPI) of a particular modulation may be shortened if there is not enoughdata to fill the entire TDU. This variability of the length of the lastTDU and PI are illustrated by the dashed lines in the last TDU and PI inFIG. 5; and the length of the last TDU and PI may be any length shorterthan, or including, their respective full ordinary lengths.

The 228-bit TDU 500 may be encoded using the well-known Reed-Solomoncoding technique to create the 300-bit PIs 520. Bandwidth needs that donot require encoding, such as the various transition gaps, arepreferably allocated in units of 1 PS. Bandwidth needs that requireencoding (using a Reed-Solomon encoding scheme, for example) may beallocated in TDUs 500. Also, data for each modulation scheme, on thedownlink, and each node's transmission, on the uplink, areadvantageously packed and fragmented to form an integer multiple of TDUs500 to create an integer multiple of PIs 520 or, alternatively, may bepacked and fragmented into an additional fractional and shortened TDU tocreate a fractional and shortened PI. The number of PSs 304, 304′required to transmit a PI 520 may vary with the modulation scheme used.An exemplary system for mapping PDUs to the PHY, and vice versa, isdescribed in detail in commonly assigned Patent Cooperation TreatyApplication Number PCTUS00/29687, entitled METHOD AND APPARATUS FOR DATATRANSPORTATION AND SYNCHRONIZATION BETWEEN MAC AND PHYSICAL LAYERS IN AWIRELESS COMMUNICATION SYSTEM (the '687 application”), which is herebyincorporated by reference. The mapping from PDU to PHY in the '687application discloses a means of converting PDUs to a form appropriatefor transmission by a wireless link. Similar systems can be used forembodiments utilizing different communications links.

FIG. 6 is an illustration of the uplink mapping of messages from PDUs toPHY elements in one embodiment. The uplink of data from upper layers tothe PHY layer may occur in the communications processors of the variousnodes served by each base station. FIG. 6 shows an example of an uplinksubframe 400 that may be adapted for use with the data transportationand synchronization process. The nodes 16 use the uplink subframe 400 totransmit information (including, for example, bandwidth requests) totheir associated base stations. There may be three or more main classesof control messages that are transmitted by the nodes during the uplinksubframe 400. Examples include: (1) those that are transmitted incontention slots reserved for node registration (Registration ContentionSlots); (2) those that are transmitted in contention slots reserved forresponses to multicast and broadcast polls for bandwidth allocation(Bandwidth Request Contention Slots); and (3) those that are transmittedin bandwidth specifically allocated to individual nodes (node ScheduledData Slots).

During its scheduled transmission time, a node typically transmits in aselected modulation that can be selected based upon, for example, theeffects of environmental factors on transmission between that node andits associated base station. The uplink subframe 400 includes aplurality of node transition gaps (NTGs) 408 that serve a functionsimilar to that of the MTs described above. That is, the NTGs 408 allowfor the transition from one node to the next during the uplink subframe400. In one embodiment, the NTGs 408 are 2 physical slots in duration. Atransmitting node 16 may transmit a 1 PS preamble during the second PSof the NTG 408 thereby allowing the base station to synchronize to thetransmission of the new node. In other embodiments, node transitions mayalternatively occur at the transition between the last PS of one node'suplink transmission and the first PS of the next node's uplinktransmission. One embodiment utilizes a system similar to that describedin the '687 application for transmitting data from nodes to a basestation; and this system and method should be understood toadvantageously utilize such a system.

As illustrated in FIG. 6, an uplink subframe 400 may comprise uplinkcontention access slots 610 as well as data slots 700. The uplinkcontention access slots 610 may include registration contention slots(not shown) and bandwidth request contention slots (not shown). Theuplink subframe 400 may begin with optional registration contentionslots, or alternatively, the registration contention slots may belocated at other points of the uplink subframe such as in the middle orat the end. Some registration contention slots are allocatedperiodically to the physical slots for use during node registration. Inone embodiment, registration messages are preceded by a 1 PS preambleand are sent alone. Also, other PDU control messages are not packed intothe same PDU. The bandwidth request contention slots may be allocatedfor responses to multicast and broadcast polls for bandwidthrequirements. In one embodiment, the bandwidth request messages, whentransmitted in the bandwidth request contention period, may be proceededby a 1 PS preamble. Nodes may pack additional bandwidth requests forother connections into the same PDU.

FIG. 6 also shows the mapping of the scheduled portion of the uplinksubframe 400. Within the subframe 400, the TC/PHY packets 700 can begrouped by nodes. All transmissions from an individual node 16, otherthan bandwidth requests transmitted in bandwidth request contentionslots, may be transmitted using the same modulation scheme. In oneembodiment, each node's transmission is packed and fragmented to be aninteger multiple of a TDUs 600 to provide an integer multiple of PIs 620after coding. In an alternative embodiment, if the bandwidth requestedfor pending uplink data does not require the entire last TDU, thebandwidth may be allocated such that the last TDU is shortened,resulting in a shortened PI. Again, this variability of the length ofthe last TDU and PI are illustrated by the dashed lines in the last TDUand PI in FIG. 6; and the length of the last TDU and PI may be anylength shorter than, or including, their respective full ordinarylengths. The uplink and downlink mapping provides a mechanism for thehigher communications protocol layers to transport data to the PHYlayer.

By using such a data transportation and synchronization technique,scheduled uplink and downlink data is transported and synchronizedbetween the PDU processing layer (discussed below as item 935 in FIG. 9)and the physical layer. The scheduled uplink and downlink data arepreferably transported within the uplink subframe 400 and the downlinksubframe 300, respectively, based upon the modulation scheme used by thenodes 16. Uplink mapping of PDUs to PHY elements may be performedaccording to the three stage process of PDU to TDU 600, then from TDU600 to PI 620, then from PI 620 to PS. However, it is to be understoodthat there are numerous processes that are analogous and similar thatmay have more or less steps and may be used. Again, the process ofconverting SDUs to PDUs is described in detail later and the mappingdescribed here provides understanding of how PDUs may be allocated toPIs in one wireless embodiment.

FIG. 7 is an illustration of an information hierarchy from sectortransmission to modulation group information to connection breakdown inan exemplary transmission link frame. FIG. 7 illustrates the wayinformation might be organized in messages sent from the base station tothe nodes. As mentioned above, the base station transmits messages tothe nodes containing three main categories of information; 1) a framecontrol header 302, containing information to the nodes concerning thehandling of the data, 2) the data 700 being conveyed from the datasources to the end users, and 3) the gaps 306, 308 that separate thedifferent sections of the transmission. The data can be broken down intothe different modulation groups such as the system illustrated by FIG. 7wherein those are the QAM-4, QAM-16, and QAM-64 modulation groups. Asystem may have more or less modulation groups. Again, the ordering ofthe modulation groups illustrated in FIG. 7 is only exemplary and anyordering or a shifting order may be utilized. FIG. 7 also illustrates aTx/Rx transition gap, or a period of time for transition from thedownlink subframe to the uplink subframe. It should be noted howeverthat the transition from downlink to uplink may alternatively occur atthe boundary between the last PS of the downlink subframe and the firstPS of the uplink subframe.

For each modulation group, the data 700 contains information for eachnode, the node data 710. As mentioned above, those nodes 16 may eitherdownload all the information or just their assigned information. Theillustration of FIG. 7, depicting the information for each node orderedin a similar manner as the modulation group, is merely exemplary aswell. The information for a particular node may also be spreadthroughout a modulation group downlink, or it may only be discretelylocated in one portion, or it may be discretely located in severalportions. The information intended for each node 16 contains informationto be distributed to the end users or services served by the connectionsof that node; this is identified in FIG. 7 as connection data 720. Theconnection data 720 includes the information to be transmitted to theusers or services as well as control information the node uses toidentify to which of its connections each packet of information shouldbe directed. Thus, the node can ensure that each of the packets ofinformation that it receives is directed to the appropriate connectionto reach the intended end user or service. In this manner, informationtransmitted by the base station 12 may logically be divided intomodulation data groups 700, and further into node data 710, and furtheryet into connection data 720. It should be noted that all of themodulation data groups 700, node data 710 groups and connection datagroups can be variable in size and may vary from frame to frame as well.

FIG. 8 is an illustration representing an exemplary PDU and illustratingthe various fields the PDU header might have. FIG. 8 shows the format ofone downlink PDU 800. Although specific fields, field lengths, and fieldconfigurations are described with reference to FIG. 8, those skilled inthe communications art shall recognize that alternative configurationsmay be used including additional or fewer fields. In severalembodiments, the communications processors of both the base station andthe nodes create PDU payloads and PDU headers to be transmitted andretrieve SDUs from received PDUs. An exemplary downlink PDU format 800may include a standard downlink PDU header 810 and a variable length PDUpayload 820. The downlink PDU header 810 of one embodiment comprises 13different fields that measure 7 bytes in total length. The downlink PDUheader 810 illustrated in FIG. 8 begins with an encryption control (EC)field. In certain embodiments, the EC field is set to a logical zero ifthe payload is encrypted; and it is set to a logical one if the payloadis not encrypted. The EC field is followed by an encryption key sequence(EKS) field that provides information about the encryption used, ifencryption is utilized. A reserved field (Rsvd) may follow the EKSfield. The Rsvd field provides for future expansion of the PDU headerfields. The Rsvd field is followed by a length field (Length). TheLength field indicates the length of the PDU header and any data maycontained in the PDU payload. The Connection Identifier field followsthe Length field and provides identification information to the basestation and the nodes. The Connection Identifier field identifies thedestination to which each PDU is to be delivered.

A header type field (HT) follows the Connection Identifier field andindicates whether the header is a standard header or a bandwidth requestheader. The HT field is followed by a convergence sub-layeridentification field (CSI) that provides information so that thecommunications processor may determine for which sub-layer, amongequivalent convergence sub-layer peers, the PDU is intended. The CSIfield is followed by a fragmentation control field (FC) and afragmentation sequence number field (FSN). These two fields allow thecommunications processor to fragment SDUs to most efficiently utilizethe payload of the PDU. The FC and FSN fields indicate the presence andorientation in the payload of any fragments of SDUs. The type offragments present in the payload and the orientation of those fragmentsin the payload may vary. For example, fragmentation may result in afragment that is the first fragment of an SDU, a continuing fragment ofan SDU or the last fragment of an SDU.

In one embodiment, a particular SDU may be large enough to requireseveral PDUs to transport it across the communications link. This SDUmay require a first PDU to convey the first fragment of the SDU, severalother PDUs to convey continuing fragments, and a final PDU to convey thelast fragment of the SDU. In this embodiment the FC and FSN bits wouldindicate that the last part of the payload of the first PDU is afragment. The FC and FSN bits of the middle PDUs would indicate thatthey contain continuing fragments in their payload and the last PDUwould have FC and FSN bits to indicate that it contains the lastfragment of a continuing SDU. The FC and FSN bits would also indicatewhere each of the fragments is in their respective PDU payload. Forinstance, the first fragment may be located at the end of the firstPDU's payload, while the continuing fragments may take up the wholepayload of their associated PDU and the last fragment may be at thebeginning of the last PDU payload. It should be noted however, that moreFC or FSN bits may be utilized to indicate any combination of types offragments present in a PDU and their locations with respect to any wholeSDUs in the payload and that the FC and FSN bits do not have to belocated in the header but may be located elsewhere.

A CRC indicator field (CI) follows the FC and FSN fields to indicatewhether or not CRC is appended to the payload. A packet discardeligibility field (PDE) can also be used and may provide informationregarding the payload in a situation where there is congestion. In acongestion situation the wireless communications system may firstdiscard packets indicating discard eligibility. A reserved field followsthe PDE field. The reserved field may provide means for future expansionof system functions. In some embodiments packing subheaders may be usedto store some header information in the payload as well; and any of theheader information may be stored in the packing subheaders. Inembodiments utilizing packing subheaders, one of the reserved bits wouldbe utilized to indicate the whether or not packing subheaders arepresent. Such a bit might be called a packing subheader present field(PSP). Packing subheaders can be of various lengths and describe thelength of the individual SDU or fragment payloads that follow eachpacking subheader. Alternative downlink PDU formats may be similar tothe downlink PDU format 800 illustrated in FIG. 8 with minor deviationsfor differing characteristics.

FIG. 9 is a functional block diagram of components in an exemplary basestation communications processor that process and transfer data. FIG. 9is a high level diagram of those functional components that process andhandle data packets being transferred from data source to user and viceversa. These functional components may be located in the communicationsprocessor of both the base station and the nodes. The higher layerinterface 910 receives the SDUs that come to the base station from thevarious data sources via the backhaul interface and the input/outputcontrol.

Alternatively, the higher layer interface 910 is part of theinput/output control. The higher layer interface 910 passes the SDUs toa classification module 920 that determines the connection (ordestination), type and size of the SDU. This determination isaccomplished using control protocols that are unique to each particularhigher layer protocol being transported. The classification data isforwarded to other base station communications processor modules tofacilitate other functions such as queuing, packing, fragmentation andassigning proper PDU header characteristics. The SDUs are then forwardedto the convergence sublayer 925 for convergence subprocessing. Theconvergence subprocesses and their service access points provide theinterfaces to higher communications protocol layers for service specificconnection establishment, maintenance and data transfer. Convergencesubprocesses of data are well-known in the art. One such convergencesubprocess is described in a text entitled “Asynchronous Transfer Mode(ATM), Technical Overview”, second edition, Harry J. R. Dutton and PeterLenhard, published by Prentice Hall, October 1995, at pp. 3-21 through3-24.

Upon processing by the convergence sublayer 925, the SDUs are ready forfurther processing. The SDUs are distinguished by their type of messageformat and their connection identification information, among otherthings as provided by the classification module. In the data queuingmodule 930 and the bandwidth allocation/process bandwidthrequest/fragmenting/packing (BPFP) module 935 the SDUs are stored andsorted based upon their individual characteristics and various systemprotocols. This information may pertain to the type of user connectionbeing served, the node the SDU is to be sent to, the type of SDU, thelength of the SDU, the available physical slots in a relevant PDU, aswell as many other factors. In one embodiment, the base station maps andallocates bandwidth for both the uplink and downlink communicationssubframes. These maps can be developed and maintained by the basestation communications control modules (conveyed in FIG. 10) inconjunction with the BPFP module 935 and may be referred to as theUplink Subframe Maps and Downlink Subframe Maps. The communicationsprocessor must allocate sufficient bandwidth to accommodate thebandwidth requirements imposed by high priority constant bit rate (CBR)services such as Tl, El and similar constant bit rate services and theirrespective formats. In addition, the communications processor mustallocate the remaining system bandwidth to mid-priority services andalso to the lower priority services such as Internet Protocol (IP) dataservices and their respective formats. In one embodiment, thecommunications processor distributes bandwidth among these lowerpriority services using various QoS dependent techniques such asfair-weighted queuing and round-robin queuing, among others.

The BPFP module 935 also utilizes the data queuing module 930 to packthe SDUs into PDUs. While the SDUs are being packed into PDUs, it may benecessary to fragment an SDU if the remaining space in the relevant PDUcannot store the whole SDU. In one embodiment, fragmentation and packingoccur cooperatively so as to maximize the benefit of each. For packingand fragmentation to occur in a cooperative manner, both processesshould occur nearly contemporaneous to one another and in accordancewith one another. If packing and fragmentation are done independently ofone another, not only may the advantages of both processes be lost, theresulting system may actually be less efficient than if only one of thetwo processes occurred. In one embodiment the packing and fragmentingprocesses occur independently of the bandwidth allocation process andsimply pack and fragment the SDUs as they are queued up by a separatequeuing process. In another embodiment the packing and fragmentationoccur in conjunction with bandwidth allocation processes and algorithmsto most efficiently utilize the communications link at any one time.Numerous queuing techniques and QoS systems may be implemented, butcertain embodiments should be flexible and allow the system controls tobe adjusted as bandwidth demands change, as connection topographychanges and as system demands change based on user requests andfeedback. The variety of system configurations available and the abilityto change as needed make such embodiments highly useful and largelyadvantageous over existing systems.

Messages now in PDU format may then be encrypted for their securetransmission. A module, such as encryption module 940, is advantageouslyprovided for this function. As discussed above with respect to FIG. 5,PDU packets may then undergo a transmission convergence (TC) process tomap the PDU packets into TC/PHY packets, or TDUs as previouslyillustrated in FIGS. 5 and 6. This process may occur in one or multiplemodules such as transmission convergence module 945. In past systems,fragmentation may have occurred in the TC process, however, suchprocessing at this stage would be independent of the packing andbandwidth allocation processes and could therefore result in a sharpdecrease in the potential benefits provided by each of those processes.The TC process may be an intermediate format as well as a couple betweenthe PDU formation and mapping to PHY elements (PIs as also mentionedabove with respect to FIGS. 5 and 6) in the physical (PHY) layer. Beyondthe TC process, the information may then be transferred to the physicallayer for further processing by the modem and the antenna, if such atransmission mechanism is utilized. This mapping of PDUs to PSs mayoccur in the transmit to PHY module 950 or any functional equivalent.

On the uplink processing of information, data is received from thetransmission mechanism and processed by the modem. The PHY receptionmodule 955 in the communications processor then receives the data in thePHY layer. The data undergoes an uplink transmission convergence, asdescribed above with respect to FIG. 6, which converts the TDU format tothe encrypted PDU format. The data may then be decrypted in a decryptionmodule 960 and passed to the BPFP module 935 for transformation from PDUpacket format back to the various SDU packet formats that wereoriginally received by the nodes from the users. The packets thenundergo the convergence process in a convergence sublayer 925 inpreparation for transport to the input/output control and on to theappropriate data source via the backhaul interface. By use of theseexemplary data handling functional modules, data is efficientlytransferred from user to data source and vice versa.

FIG. 10 is functional block diagram of components that handle controlfunctions in an exemplary base station communications processor. Thebase station communications controls for an ATDD embodiment areillustrated in FIG. 10 and contain information and process controlfunctions for each of the nodes, all of the individual communicationslinks, and all of the system functions in order to effectively monitor,operate and optimize the communications system performance. Thefunctional modules illustrated comprise only a high level description ofexemplary control functions and there are many other functions that mayoccur in the control of a communications system that, for brevity, arenot described herein. However, one skilled in the art will appreciatethat such functions can be used in such a system.

Communications link connection setup information, maintenanceinformation and performance information can be collected and processedduring system operation, and this is advantageously performed byconnection establishment and maintenance module 1010. In one embodiment,the number of communications links, should change infrequently as thenumber of nodes operating in any one sector may rarely change, while thenumber of connections to those particular nodes may change more rapidly.However, some embodiments may be ideally suited for those systems whosenumber of links rapidly change and also for those systems that rarelyadd or drop nodes. The power of the transmitting signal between the basestation and the node can be controlled as well to maximize both signaleffectiveness and efficiency. A power control module 1020 determines themost appropriate power level at which each node should transmitcommunications signals on the uplink. The SNR/BER calculation module1030 can constantly measure the quality of the signal being transmittedbetween the base station and the nodes to determine if acceptable signalquality levels are being maintained. If not, any number of controlparameters may be changed to correct the problem. The type of forwarderror correction, modulation, or power level utilized for thetransmission of the information, among numerous other parameters, may bechanged to correct any signal deficiencies.

An adaptive burst profile management module 1080 and an ATDD managementmodule 1060 are used to control the ratio of uplink to downlink slots ineach frame 202 and provide control information to the BPFP module 935 toassist its bandwidth allocation functions. A node state managementmodule 1040 stores and utilizes information about each node to provideinput into numerous control functions, such as bandwidth allocation, QoSprotocol, transmission signal optimization, connection identification,and many others. As mentioned before, these exemplary controls may beutilized in embodiments practicing the current invention, but many otherfunctions may also exist and are not mentioned here.

FIG. 11 is a functional block diagram of components that process andtransfer data in an exemplary node communications processor 32. FIG. 11is a high level diagram of those node communications processorfunctional components that process and transfer SDUs from the users tothe data sources and vice versa. The higher layer interface 1110receives the SDUs that come to the node from the various connections viathe connection interface. Alternatively, the higher layer interface 1110may be part of the connection interface. The higher layer interface 1110transfers the information to a classification module 1120 thatdetermines the characteristics of the SDUs to be forwarded to the basestation. This determination is accomplished using control protocolsunique to each particular system and provides classification datanecessary to correctly transfer each SDU to its respective data source.As stated above, the classification data is forwarded to othercommunications processor modules to facilitate functions such asqueuing, packing, fragmentation and assigning proper PDU headercharacteristics. The SDUs are then transferred to the convergencesublayer 1125 for convergence subprocessing. As discussed above,convergence subprocessing allows various connection types from higherlevel communications access points to interface with the lower layers ofthe communications system. The convergence subprocesses of the node aresimilar to the convergence subprocesses previously described withrespect to the base station. After convergence, the user data istransferred to the queuing module 1130 for arrangement and storing,similar to that in the base station described above, in preparation fortransfer to the bandwidth allocation/create bandwidthrequest/packing/fragmentation (BCPF) module 1135. This module sorts dataaccording to connection type and various types of priority informationstored within the system to determine queuing order of the various datapackages. The data packages are then sequentially fitted into PDUpackets as previously discussed. Again, the data packets areadvantageously packed and fragmented in a coordinated manner and in themost efficient way possible to maximize the bandwidth available fromframe-to-frame.

Again, it is advantageous to incorporate the packing and fragmentationprocesses with the bandwidth allocation process so as to maximize theflexibility, efficiency and effectiveness of both fragmentation andpacking.

The SDUs, after data queuing 1130 and conversion into PDUs by BCPFmodule 1135 processing, are transferred to the encryption module 1140.The encryption module can encrypt the PDUs for secure transmission, in asimilar manner as that described above for the base station. EncryptedPDUs are then transmitted to the physical layer by undergoing a TCprocess in transmission convergence module 1145, similar to thatdescribed above in producing TDUs. Transmission to the physical layer iscompleted by physical layer module 1150, which maps the TDUs to the PIsas before. Upon transmission to physical layer, the PIs are then readyfor transmission via modern, IF/RF converter and antenna to the basestation, where they are processed as previously discussed and thentransferred to the appropriate data source.

When data on the downlink is transmitted from the base station to thevarious nodes, it is received via antenna and processed by IF/RFconverter modem, if such an embodiment is utilized, and arrives at thereceive from physical layer module 1155. Here, the data is received asPIs and is converted to TDUs and then undergoes a transmissionconvergence 1145, as previously discussed, converting received TDUs intoencrypted PDUs. The encrypted PDUs are then passed through decryptionmodule 1160 and then are processed by unpacking and defragmentationmodule 1170, which converts them back into the SDU format they were inwhen they arrived at the base station from the data source. Uponconversion back into the SDU format, the SDU packets then undergo aconvergence process in the convergence sublayer module 1125 forcommunications via the higher layer interface 1110. In the higher layerinterface 1110, the SDUs are directed to their respective connectionsthrough the connection interface, from where they are passed on to theirrespective connections, or users.

FIG. 12 is functional block diagram of components that handle controlfunctions in an exemplary node communications processor. FIG. 12illustrates some of the communications control modules that may be usedby the nodes in establishing and maintaining transmission links with thebase station. As mentioned before, these exemplary communicationscontrol modules are only provided for illustrative purposes, as more orfewer may be used. It is understood that other functions may beaccomplished by the node communications processor that are not includedin the subsequent discussion, yet those of skill in the art understandthose functions to be incorporated herein. Similar to that of the basestation, a connection establishment and maintenance module 1210 may beutilized to establish the communications link between the node and thebase station. The node's communications processor may include othermodules that also correspond closely to the base station communicationscontrol modules and perform similar functions. These modules may includea power control module 1220, a SNR/BER calculation module 1230, a nodestate management module 1240, and an adaptive burst profile managementmodule 1280, among others.

These modules can perform functions that correspond to, and arecomplimentary with those of the base station communications controlmodules described above. The power control module 1220 may utilizesignals sent by the base station to adjust the node's transmission powerlevel as necessary to optimize the communications link's performance.The SNR/BER calculation module 1230 can interact with signals from itscomplimentary base station control module to monitor the performance ofthe communications link and to request the base station to adjust thedownlink transmission characteristics as necessary to optimize thatperformance. The node state management module 1240 can maintaininformation about the node and the communications link between the nodeand the base station and may transfer information as necessary to updatesuch information that is stored in the base station. An adaptive burstprofile management module 1280 may also be utilized to correspond withthat of the base station to adaptively change uplink burst profile. Inaddition, the node communications controls may also include variousoperational parameter control modules such as automatic frequencycontrol (AFC) and automatic gain control (AGC) control module 1190 thatcan control various settings of the modem used in the communicationssystem.

FIG. 13 is a flow chart illustrating the steps of an exemplary processfor forming PDUs from incoming SDUs. The process 1300 in FIG. 13illustrates the coordination of the fragmentation and packing processesthat the communications processors may utilize in one embodiment of boththe base station and the nodes. An SDU or fragment that is next in thequeue is identified and obtained at state 1310; then the process movesto decision state 1315. At decision state 1315, the communicationsprocessor decides whether the SDU or current fragment is larger than theavailable bits in the payload of the current PDU. If the current SDU orfragment is larger than the available PDU payload, the process moves tostate 1320. At state 1320, the SDU or fragment is fragmented and mappedto fill the current PDU. The process then moves to state 1325. At state1325, the remaining fragment of the current SDU is buffered and can bemapped into the next successive PDU, and the process moves to state1330. At state 1330, the fragmentation control bits in the PDU headerare adjusted to indicate the presence and orientation of fragments inthe PDU. The process then moves to state 1335 where the PDU header isupdated to incorporate information regarding the payload it carries,which may include the length and the presence or absence of a packingsubheader. The process then moves to state 1340. At state 1340, the PDUis mapped to the physical layer and transmitted either from the node tothe base station, or from the base station to the node. The process thenmoves to state 1345. State 1345 is a transitional state to the next PDUso that the next PDU is formed in the communications processor. Theprocess then moves back to state 1310 where the next SDU or fragment inthe queue is mapped according to the same process 1300.

Going back to decision state 1315, if the current SDU or fragment is notlarger than the available bits in the current PDU payload, then theprocess moves to state 1350. At state 1350, the SDU or fragment ismapped to the current PDU. The PDU header is then updated in state 1355.The process then moves to decision state 1360. At decision state 1360,the communications processor determines whether there are any availablebits remaining in the current PDU. If there are available bits, theprocess then returns to state 1310 to obtain the next SDU or fragment inthe queue. If there are no more available bits in the PDU, then theprocess moves to decision state 1365. At decision state 1365, thecommunications processor determines whether there are fragments presentin the PDU. If there are fragments present in the PDU, the process thenmoves to state 1370. The fragment control bits are then adjusted toindicate the presence and orientation of those fragments. The processthen moves to state 1340 for PDU transmission and then returns, asbefore, via state 1345 to the beginning state 1310 where the next SDU orfragment is queued up. If there were no fragments present in the presentPDU at state 1365, then the fragment control bits are adjusted toindicate such absence and the process moves from state 1365 to state1340 for PDU transmission and then onto state 1345 to create the nextPDU. Through this process, PDUs are created from SDUs via afragmentation and coordinated packing process. By coordinating thefragmenting and packing processes that occur in the bandwidth allocationprocess, rather than the convergence sublayer, the advantages of packingand fragmentation are optimized and maintained whereas the efficiencygained by both processes may be lost if they were performedindependently of one another.

FIG. 14 is an illustration demonstrating the relationship between thePDU header, the payload and the packing subheader. FIG. 14 illustratesthe packing of multiple variable length SDUs into a single PDU. Theembodiment illustrated in FIG. 14 is intended to correspond with the PDUheader described previously with respect to FIG. 8. However, only thelength field and the packing subheader fields described above aregermane to the current discussion. An exemplary PDU 1400 contains twomain sections, a PDU header section 1402 and a PDU payload section 1420.The PDU header section 1402 can include the various components that makeup the header section described in FIG. 8. As can be seen in FIG. 14,the parts of the PDU header section 1402 illustrated include a lengthfield 820 and a packing subheader present 819 field. The PDU lengthfield 820 has a sample entry of J and a sample packing subheader presententry 819 of 1 meaning, in this case, that the length of the payload isgoing to be J and there are packing subheaders 1404, 1410, 1414, presentin the payload. Packing subheaders 1404, 1410, 1414, occur in thepayload of the PDU packet 1400 and they can occupy a variable number ofbits depending on the type of information they contain and the lengthsof the corresponding SDUs that follows the packing subheaders 1404,1410, 1414.

The packing subheaders 1404, 1410, 1404, may include, among other items,a length extension item (LE) and a length item. The length extensionitem indicates the quantity of bits required in the subheader lengthfield to indicate the length of the SDU that follows the subheader. Thelength item indicates the length of the SDU. There may be multiplevariable length SDUs between the second variable length SDU 1412 and afinal variable length SDU 1416; or there may be no more SDUs between thetwo. The PDU header 1402 contains a length field J that comprises theentire length of the payload 1420. That payload 1420 includes the lengthof the first SDU 1408 (length a), the length of the second SDU 1412(length b), the length of the last SDU 1416 (length c) as well as thelengths of the respective packing subheaders 1404, 1410, 1414, and anyother SDU lengths and their subheaders that are in the payload 1420. Bythis system, various lengths can be utilized and accommodated whileminimizing the amount of payload 1420 bits that are utilized in thepacking subheaders 1404, 1410, and 1440. Because the packing subheadersize can be variable depending on the type of information it containsand the length of the SDU with which it corresponds, the amount ofpayload lost, or that is not dedicated to carrying data, is minimized,while still allowing the PDU to contain variable length SDUs in the mostefficient manner.

Through the components and functions described in the precedingparagraphs, a system and method are described that utilize packing andfragmentation in an efficient manner. In certain embodiments the packingand fragmentation processes are implemented in a cooperative manner tofully realize the benefits of both. Additionally, it is advantageous tocoordinate packing and fragmentation with bandwidth allocation so that acommunications system can be most flexible and able to capitalize on thecircumstances that may exist in any one communications cycle. Thissystem also utilizes a method of packing variable length SDUs that isadvantageously adaptive. Through the use of variable length packingsubheaders the amount of available payload that is lost in describingthe data carried within it, or cell tax, is minimized further improvingthe effectiveness and efficiency of the packing process. It isunderstood that the description was mainly made with respect to awireless data communications system. However, as stated previously, thisdescription applies to all packeted data communications systems and itmay be advantageously utilized in any one of the previously mentionedtypes of communications systems.

The foregoing description details certain embodiments of the invention.It will be appreciated, however, that no matter how detailed theforegoing appears in text, the invention can be practiced in many ways.As is also stated above, it should be noted that the use of particularterminology when describing certain features or aspects of the inventionshould not be taken to imply that the terminology is being re-definedherein to be restricted to including any specific characteristics of thefeatures or aspects of the invention with which that terminology isassociated. The scope of the invention should therefore be construed inaccordance with the appended claims and any equivalents thereof.

1. A base station that communicates over a wireless communication linkwith mobile subscriber units, comprising: one or more processorsoperable to, establish a service connection from the base station to amobile subscriber unit, map variable length service data units (SDUs)associated with the service connection into variable length protocoldata units (PDUs) associated with the service connection, the SDUs beingmapped into the PDUs based at least in part on data carrying capacityprovided by the base station for transmission to the mobile subscriberunit in a physical downlink frame, the data carrying capacity based onat least one of a priority associated with the service connection, amodulation scheme and an error correction scheme, and map the PDUs forthe mobile subscriber unit into the physical downlink frame; and atransmitter operable to transmit the physical downlink frame over thewireless communication link using the modulation scheme and the errorcorrection scheme.
 2. A base station in a wireless communication system,comprising: one or more processors; a computer readable storage mediumstoring instructions which when executed by the one or more processorscause the one or more processors to establish a service connection fromthe base station to a mobile subscriber unit, map variable lengthservice data units (SDUs) associated with the service connection intovariable length protocol data units (PDUs) associated with the serviceconnection, based at least in part on data carrying capacity providedfor transmission to the mobile subscriber unit in a physical downlinkframe, the data carrying capacity based on at least one of a priorityassociated with the service connection, a modulation scheme and an errorcorrection scheme, and map the PDUs for the mobile subscriber unit intothe physical downlink frame; and a transmitter operable to transmit thephysical downlink frame to the subscriber unit using the modulationscheme and the error correction scheme.
 3. A method for operating a basestation in a wireless communication system, comprising: establishing aservice connection from the base station to a mobile subscriber unit;mapping variable length service data units (SDUs) associated with theservice connection into variable length protocol data units (PDUs)associated with the service connection, based at least in part on datacarrying capacity provided for transmission to the mobile subscriberunit in a physical downlink frame, the data carrying capacity based onat least one of a priority associated with the service connection, amodulation scheme and an error correction scheme; mapping the PDUs forthe mobile subscriber unit into the physical downlink frame; andtransmitting the physical downlink frame to the subscriber unit usingthe modulation scheme and the error correction scheme.